Some internal combustion engines are equipped with electric valve actuators that can be operated to vary the position of an intake or exhaust valve of an engine cylinder. Some electric valve actuators may include a spring that biases the valve at a particular equilibrium position. In order to move the valve relative to the equilibrium position, a current may be supplied to a magnetic coil of the actuator. In some conditions, a minimum or base level of current may be applied to the actuator to hold the valve in a particular position away from the equilibrium position. However, identifying the base level of current for a valve may be difficult due to variations in valve construction and/or changing operating conditions of the valve. Likewise, individually testing each actuator before installation may be impractical or costly.
In one approach, a common level of current for some or all of the electric valves of a set may be identified by determining the highest base current or upper limit of the tolerance of all of the electric valve actuators of the set. The common level of current may then include at least the highest base holding current of the set and may include an additional amount of current to provide robust operation.
However, the inventors herein have recognized that some issues may exist with the above approach. Specifically, a common holding current delivered to two or more valve actuators may result in a higher level of current than is necessary for some of the actuators to maintain a particular holding position. This additional current supplied to the actuators may serve to increase the power consumed by the electric valve actuation system, during some engine conditions. Further, differences between the base level of current for holding the valve actuator and the assigned common level of current may cause variations from actuator to actuator in the time delay between a valve command and physical movement of the valves. These variations in response time may, in at least some cases, degrade engine performance or efficiency.
In a first approach, as described herein, the above issues may be addressed by A method of operating an engine having at least one cylinder, said cylinder including at least one electric valve actuator, said actuator including at least a coil and an armature moveable thereto, the method comprising: during a non-firing state of the cylinder:
holding the armature of the actuator at a first position away from an equilibrium position by supplying a first amount of current to a first coil of the actuator; and reducing current supplied to the first coil from said first amount to a lower second amount to cause the armature to begin moving toward the equilibrium position; and during a subsequent firing state of the cylinder, varying an amount of holding current supplied to the first coil for holding the armature away from the equilibrium position based on at least said second amount of current.
In this way, a valve actuator may be operated at or near its particular base holding current in response to a condition of the particular actuator that is identified before combustion is initiated in the engine or cylinder thereof. Thus, degradation of engine performance and/or efficiency may be reduced.
Note, that this approach may be applied independently to each coil of the actuator to identify a different holding current for the open position and closed position of the valve. Further, the above approach may be applied over successive cylinder shut-downs while other cylinders are operating such as with a variable displacement engine or during an engine shut-down such with a hybrid electric vehicle (HEV) utilizing period engine shut-off to conserve energy. In this manner, the holding current of the valve actuator may be updated as operating conditions of the actuator change with time, due to temperature, aging, etc.
Further still, the above approach may be used together or independently with other approaches described herein to further reduce power consumption of the electric valve actuation system and/or to reduce delay variance between valves. Still other approaches described herein may be used to provide a sufficient holding current while reducing delay variations among valves and increasing efficiency of the valve actuation system.